The oligomerization of olefin compounds is conventionally accomplished by catalytic reaction. Oligomerization catalysts are typically nickel based catalysts or acid based catalysts. Generally, oligomerization processes which use nickel based catalysts are carried out by forming a homogenous suspension of catalyst, olefin feed and product, whereas the acid based catalyst systems are carried out using a flow-through, fixed bed type of arrangement. The homogeneous suspension type of system is generally much more technically difficult to operate, but offers certain advantages in its ability to produce a greater degree of “semi-linear” oligomer products. These semi-linear products are products with limited branches, and can be beneficial in certain uses such as further reaction to form plasticizers, solvents or diesel type fuels in which limited branching is desirable.
Cosyns, J. et al., in “Process for upgrading C3, C4 and C5 olefinic streams,” Pet. & Coal, Vol. 37, No. 4 (1995), describe a nickel based catalyst system known as the Dimersol® process. This process is useful for dimerizing or oligomerizing a variety of olefin feeds. In particular, the process is useful for dimerizing or oligomerizing propylene, butylene and pentylene streams.
U.S. Pat. No. 6,143,942, to Verrelst et al., describes the oligomerization of C2 to C12 olefins using a mixture of ZSM-5 and ZSM-22, and ZSM-57 and ZSM-22. The particular combination of catalysts produces a high yield of trimer products.
U.S. Pat. No. 5,874,661, to Verrelst et al., describes a system for reducing branching of oligomerized olefins. In this system, lower olefins, such as propene or butene, are oligomerized to an oligomer or higher olefin using an acid based catalyst such as ZSM-5. The higher olefin is then isomerized also using an acid based catalyst, such as ZSM-5 or ZSM-22, to isomerize the higher olefin and reduce the degree of branching. The isomerized higher olefin is then hydroformylated to form surfactants and polyolefin stabilizers.
U.S. Pat. No. 5,762,800, to Mathys et al., describes a process for oligomerizing C2 to C12 alkenes using a zeolite oligomerization catalyst. The catalytic life of the catalyst is increased by hydrating the olefin feed to the oligomerization reactor.
U.S. Pat. No. 6,049,017, to Vora et al., describes the dimerization of a predominantly n-butylene containing feed stream. The n-butylene feed stream is ultimately derived from an olefin stream containing a variety of butylenes produced by a methanol to olefins reaction unit. The butylene stream from the methanol to olefins unit is pretreated by a combination of partial hydrogenation of dienes and isobutylene removal by way of an MTBE process, before sending the resulting n-butylene stream to the dimerization unit.
Often, efficiency of the oligomerization process is reduced due to the presence of greater than desirable quantities of inert components in the feed stream; for example, paraffins such as propane and butane. These inert components, in essence, take a free ride through the reaction system, taking up valuable reactor volume without being reacted to desirable products. Therefore, multiple separation processes to remove inert components are often required.
Olefin feed streams can also contain contaminants that act as poisons to oligomerization catalysts. For example, nickel based oligomerization catalysts are quite sensitive to sulfur and nitrogen. Such contaminants can have a particularly significant impact on the active life of the catalyst, shortening the life of the catalyst to the point where the reaction process is not feasible to operate.
It is, therefore, desirable to find oligomerization catalysts that are less sensitive to olefin feeds having higher concentrations of oxygenate contaminants. It is also desirable to operate such processes to prevent higher concentrations of olefin feed contaminants from causing significant operating problems. In this regard, it would be particularly desirable to take advantage of an olefin feed stream which needs little to no pretreatment for use in an oligomerization system.